A Bronx mother fatally shot her 12-year-old son in the head before blowing her brains out in what cops believe is a murder-suicide.

Micaela Jackson, 37, was found with the 9mm weapon still in her hand, lying in the same bed as her son, Kenneth Holmes, Jr., sources said.

“He was a gift, he was pure,“ said the boy’s devastated father, who shares the same name as his son.

“It doesn’t make any sense to me, his mother was so strong.

“I don’t know what would make her want to do that.“

The tragedy was discovered yesterday when Jackson’s sister grew concerned after not hearing from her in a while and went to the Morris Heights home around 7:25 p.m. to see her.

The first-floor Loring Place apartment was locked and chained from the inside, so the increasingly worried sibling got the building’s superintendent to open the door.

That’s when they made the grisly find – which came less than a week after a Staten Island mother, Leisa Jones, slit three of her children’s throats and then killed herself and her two-year-old son by setting their apartment on fire.

Jackson and her son, who was autistic, lived by themselves.

Sources said investigators were not looking for any suspects.

The bloodshed left several teary-eyed relatives at a loss to explain why Jackson would murder her child.

Holmes Sr. said Jackson had recently been promoted at Montefiore Hospital, where she had been working as a secretary.

He added that they all enjoyed a recent family trip to Rye Playland.

“She was at a happy point in her life,“ he said.

A woman who identified herself as a cousin said, “She was a good person, I don’t know what happened.

“She was a really great mom and the family is grieving right now.“

The heartbroken dad said he saw his son every Sunday and the child, “had a great smile and a lot of charm.